1. Field of the Invention
The present invention relates generally to endoluminal tubular prostheses, such as stents, stent-grafts, and other structures. More particularly, the present invention provides bifurcated prosthesis structures having properties which are tailored for individual body lumens, including blood vessels, particularly for the treatment of abdominal and other aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending distally into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper sizing of endovascular prostheses can be problematic.
Proper matching of the prosthesis to the branching blood vessel is critical to the treatment of an aneurysm. The prosthesis preferably extends axially beyond the weakened portion of the blood vessel to anchor securely in the healthy vessel wall. However, the cross-sectional size and axial length of individual blood vessels vary considerably between patients. Even within a patient, the cross-section and resilience of a lumen wall can vary considerably along its axial length, and the location and extent of the aneurysm will differ with different patients. Additionally, each prosthesis must be carefully constructed and handled, making it extremely costly to provide and maintain the large selection of prostheses required for proper fitting of every individual patient.
Known branching intraluminal prostheses are generally formed as tubular, radially-expandable stent-grafts. These stent-graft structures have typically been formed with simplistic cylindrical frames or “stents”. A separate liner or “graft” is typically attached to the frame to prevent blood flow through a ruptured vessel wall. Such liners are often formed from inelastic textiles to prevent pressure from distending a weakened luminal wall. These branching textile liners have often been woven as continuous branching tubes to avoid any seams or joints which might fail after the stent-graft has been positioned. Unfortunately, this has also resulted in branch perimeters which are each a fraction of the perimeter of the liner at the common lumen, each branch typically being half the common lumen in diameter. This does not accurately reflect the relative sizes of branching body lumens. Hence, some mismatch are inevitable when using the proportional branching stent-grafts of the prior art.
Another problem associated with the branch stent-grafts of the prior art is that these known cylindrical structures generally form parallel branches when at rest, while the branches of body lumens often separate at significant branching angles. Although it is possible to deform a straight branching prosthesis, the imposition of such axial bends on endovascular stent-grafts tends to cause folding and/or wrinkling which occlude their lumens and degrade their therapeutic value.
Still another disadvantage of known bifurcated stent-grafts is that they often result in an imbalance in flow area to the different branches. Existing stent-grafts often rely, for at least some distance, solely on the liner material to maintain separation between branching lumens. Such an external frame structure to support an internal flexible liner, although effective at holding the total liner lumen open, does not provide a fixed separation between lumens. Instead, the liner material often pushes over to one side or the other. Although it is possible to separate the lumens with a portion of the frame, compression of such dual lumen frames is problematic, and would increase the total compressed diameter of branching prostheses.
For these reasons, it would be desirable to provide improved branching endoluminal prostheses, including stents and stent-grafts, and improved methods for placement of such endoluminal prostheses to treat aneurysms and other conditions. It would further be desirable to provide endoluminal prostheses which match the actual luminal geometries of blood vessels and other body lumens without compromising their therapeutic effectiveness. It would be particularly desirable to provide adaptable prostheses and methods for their replacement which would facilitate effective treatment of widely varying luminal system geometries without requiring an excessive inventory of prostheses to choose from.
2. Description of the Background Art
Copending U.S. patent application Ser. No. 08/538,706, the full disclosure of which is hereby incorporated by reference, describes modular prostheses and constructions methods which are particularly advantageous for use with the bifurcated prostheses of the present invention.
U.S. Pat. No. 5,064,435 describes a self expanding prosthesis which maintains a stable axial length during expansion by anchoring of radially outward flares at each end, and by sliding of an overlapping medial region therebetween.
Vascular grafts and devices for their endoluminal placement are described in U.S. Pat. Nos. 5,282,824; 5,272,971; 5,242,399; 5,219,355; 5,211,658; 5,201,757; 5,192,297; 5,190,058; 5,158,548; 5,147,370; 5,104,399; 5,092,877; 5,078,726; 5,019,085; 4,990,151; 4,950,227; 4,913,141; 4,886,062; 4,820,298; 4,787,899; 4,617,932; 4,562,596; 4,577,631; and 4,140,126; and European Patent Publications 539,237; 533,511; 518,839; 518,704; 508 473; 505,686; 466 518; and 461 791. Catheters for placing vascular stents are described in U.S. Pat. Nos. 5,192,297; 5,092,877; 5,089,005; 5,037,427; 4,969,890; and 4,886,062. Catheters carding a graft structure in a tube or capsule are described in U.S. Pat. Nos. 5,275,622; 5,104,399; and 4,787,899; and EP466518.